The invention relates to a surgical instrument for tensioning two plate-shaped engaging elements with respect to each other at opposite sides of bone portions, a first engaging element carrying next to each other at a spacing from each other two pin-shaped or rod-shaped connecting members which pass through openings in the second engaging element, with a supporting surface for engagement on the side of the second engaging element that faces away from the first engaging element, and with a tensioning device engaging the connecting members for displacement of the connecting members and consequently of the first engaging element in the direction towards the second engaging element.
Such an instrument is known from DE 197 00 474 and also from DE 103 10 004 B3. However, these are both configured for gripping only a single pin-shaped connecting element. An instrument is described in DE 20 2006 007 221 U1, in which the engaging elements can also be tensioned with respect to each other in an implant having two pin-shaped connecting elements arranged next to each other. To bring about the tensioning, the instrument engages a bridge which rigidly connects the two pin-shaped connecting elements to each other at their free ends. The two plate-shaped engaging elements are thereby inevitably displaced parallel to each other when the tensioning device is actuated, so that the engaging elements are unable to follow a structure of the bone plates accommodated between them, which is not exactly parallel. This results in different values of the contact pressure of the engaging elements on the bone portions lying between them and, consequently, in different tensions. Such an uneven distribution of tensions may prove unfavorable.
The object underlying the invention is to enable, in a generic instrument for tensioning engaging elements with respect to each other, which have two connecting members arranged next to each other, an adjustment of the engaging elements to different shapes and thicknesses of the bone portions lying between the engaging elements, which results in a distribution of the pressing forces which is as even as possible over the entire surface of the engaging elements.